1. Field of the Invention
The present invention relates to a circuit for a matrix calculation of the discrete cosine transformation (DCT). The circuit according to the present invention is used for an orthogonal transformation unit in a picture image processing device in a video transmission system. The circuit for a matrix calculation of the discrete cosine transformation is useful for high efficiency coding in a video transmission system.
2. Description of the Related Art
In general, the matrix calculation circuit of the discrete cosine transformation is constituted by, for example, 8 multipliers and 8 summing devices, the number of the multipliers is the same as the number of summing devices. Received input data X.sub.11 is multiplied by transformation coefficients of the discrete cosine transformation d.sub.11, d.sub.21, d.sub.31, . . . read from a read only memory for storing the transformation coefficients. The results of the multiplication X.sub.11 d.sub.11, X.sub.11 d.sub.21, X.sub.11 d.sub.31, . . . are registered in registers connected to the summing devices.
The next received input data X.sub.21 is multiplied by transformation coefficients of the discrete cosine transformation d.sub.12, d.sub.22, d.sub.32, . . . read from the read only memory for storing the transformation coefficients. The results of the multiplication X.sub.21 d.sub.12, X.sub.21 d.sub.22, X.sub.21 d.sub.32, . . . are added to the results of the preceding multiplication X.sub.11 d.sub.11, X.sub.11 d.sub.21, X.sub.11 d.sub.31, . . . registered in the registers, and the results of the summation are stored in the registers to achieve a cumulative summation. The calculation is repeated 8 times to obtain the elements y.sub.11, y.sub.12, . . . y.sub.18 of the matrix. These calculations are further repeated 8 times to obtain all elements y.sub.11, y.sub.12, . . . y.sub.88 of the matrix. Thus, an 8.times.8 matrix calculation of the discrete cosine transformation [Y]=[D].times.[X] is completed.
However, in said matrix calculation circuit of the discrete cosine transformation, it is necessary to provide a number of summing devices equal to the number of multipliers, and accordingly the scale of the circuit increases. Since a multiplier has a relatively large number of gates, the scale of the gate of the entire calculation circuit is increased, which causes an undesirable increase in scale for constituting a matrix calculation circuit of the discrete cosine transformation of the large scale integrated type circuit.